1. Field of the Invention
The present invention relates to ribbon microphones and ribbon microphone units.
2. Related Background of the Invention
A ribbon microphone includes a magnet for forming a magnetic field and a ribbon diaphragm, as main component members. The magnet is disposed on both sides of the ribbon diaphragm to sandwich the same, whereby a magnetic field is formed between the magnets on the both sides. The ribbon diaphragm is given an appropriate tension and disposed within the magnetic field while the both longitudinal ends are held down. In response to a sound wave, the ribbon diaphragm vibrates within the magnetic field and thereby a current corresponding to the sound wave flows through the ribbon diaphragm and thus the sound wave is converted into an electric signal. Generally, an aluminum foil is used as the material of the ribbon diaphragm. Since aluminum has an excellent electrical conductivity as compared with other metallic materials and also has a low specific gravity, aluminum is suitable as the ribbon diaphragm of the ribbon microphone.
The ribbon microphone is a mass control type microphone, and in the reproduction limit of the low frequency side, the lower the resonance frequency of the ribbon diaphragm, to the lower frequency the sound signal can be electroacoustically transduced. However, if the resonance frequency of the ribbon diaphragm is too low, such a problem will occur that the ribbon diaphragm easily moves to contact a pole for forming the magnetic field when a wind blows against the ribbon diaphragm or when a vibration is applied thereto. For this reason, in order to attach the ribbon diaphragm, it is necessary to pull the both longitudinal ends with an appropriate force, fix the both ends under an appropriate tension, and increase the resonance frequency to an appropriate frequency.
Then, in the manufacture process of the conventional ribbon microphone or in the adjustment process thereof, an operator lightly blows on the ribbon diaphragm, and visually observes and checks the bending level of the ribbon diaphragm at that time, and then adjusts the tension to an appropriate one. As described above, an aluminum foil is suitable for the ribbon diaphragm of the ribbon microphone. However, since the aluminum foil is extremely thin and light weighted, it may break when provided in a tensioned state while the tension is adjusted. Accordingly, good or poor results of the product largely depend on the skills of an operator, so a lot of skills are required in order to manufacture an excellent ribbon microphone.
Although the present invention relates to the ribbon microphone, the structure is similar to the structure of a ribbon speaker. In the ribbon speaker, a signal current is passed through a ribbon diaphragm, and then cooperating with a magnetic field which a magnet generates, the ribbon diaphragm is vibrated to generate sounds. Hereinafter, the inventions described in Patent Documents related to the present invention, including the ribbon speaker, will be described.
The invention described in Patent Document 1 relates to a tension adjustment method of a ribbon diaphragm of a ribbon microphone. This conventional ribbon microphone unit comprises a yoke formed into a square frame, and a ribbon diaphragm disposed along the longitudinal direction of the yoke and in the center portion in the width direction of this yoke. The yoke integrally includes a support plate near the both longitudinal ends, and a presser plate is disposed on the lower surface side of these support plates, respectively. The presser plate is secured to the support plates by fastening a screw, respectively. This screw is adjusted so as to lightly press the ribbon diaphragm in advance, and then the ribbon diaphragm is vibrated by a vibrator, and while observing its amplitude, the tension of the ribbon diaphragm is adjusted, and then by fastening the screw the ribbon diaphragm is secured. Since the screw is used as a securing unit of the ribbon diaphragm, the tension adjustment of the ribbon diaphragm can be carried out repeatedly.
The invention described in Patent Document 2 relates to a method of assembling a diaphragm assembly including a ribbon diaphragm used for a ribbon speaker. This conventional example comprises: a ribbon diaphragm that is wound in a roll form; a magazine component in which a slit is formed in the longitudinal direction and an adhesive layer is formed in the surface thereof; and a pressure roller wider than the slit. The above-described magazine component is made up of a nonmagnetic aluminum material, and the ribbon diaphragm is disposed parallel to the longitudinal direction of the slit. In the method of assembling the diaphragm assembly, while moving the magazine component in the longitudinal direction, the ribbon diaphragm is continuously pressure-welded to the magazine component via the adhesive layer by the pressure welding of a pressure roller, and thereby the both longitudinal ends of the ribbon diaphragm are bonded to the magazine component. According to the method of assembling the diaphragm assembly, which is a conventional example, the failure rate of the ribbon diaphragms caused by a manual assembly can be reduced, and the diaphragm assembly can be manufactured automatically and continuously.
The invention described in Patent Document 3 relates to a ribbon speaker. This conventional example comprises: a yoke, wherein a magnetic gap-forming portion of the yoke that constitutes a magnetic circuit together with a magnet is divided; and a vibration-system assembly provided with a ribbon diaphragm. The vibration-system assembly functions as a spacer, which prevents the divided yokes from contacting to each other by interposing a nonmagnetic material, e.g., an aluminum material, between the divided yokes. Moreover, by interposing the vibration-system assembly within the parallel magnetic field generated between the divided yokes, excellent frequency characteristics can be obtained. A signal current is passed through the diaphragm provided in the vibration-system assembly to vibrate the diaphragm, thereby outputting a sound. The vibration-system assembly can be detached by disassembling each of the divided yokes. Accordingly, when the diaphragm is damaged, the repair of the damage or the component replacement can be easily carried out by detaching the vibration-system assembly.
The invention described in Patent Document 4 relates to a ribbon speaker. Both ends in the axial length direction of a ribbon diaphragm are supported with a stationary terminal, and at the same time an ultraviolet curing resin is applied to the edge in the axial length direction and to the wall surface of a plate disposed within a magnetic gap, in which the ribbon diaphragm is disposed. Then, the ultraviolet curing resin is irradiated with an ultraviolet ray and is reacted, and thereby the diaphragm is attached to the inside of the magnetic gap of the magnetic circuit. The air-setting adhesive has a drawback that a long curing time and also an unstable cured state due to the variation in the curing conditions affect the performance of the ribbon diaphragm. In contrast, in the ultraviolet curing resin, a portion coated with the ultraviolet curing resin is irradiated with an ultraviolet ray, thereby eliminating a non-uniformity or variation in the cured state or curing time and thus obtaining a stable cured state.
[Patent Document 1] Japanese Unexamined Patent Application Publication No. 2006-319595
[Patent Document 2] Japanese Unexamined Patent Application Publication No. S57-171900
[Patent Document 3] Japanese Unexamined Utility Model Application Publication No. S57-163892
[Patent Document 4] Japanese Unexamined Utility Model Application Publication No. S57-119989